1. Field of the Invention
This invention relates generally to pressure relief valves for fluid storage tanks and, more particularly, to such a valve which includes a snubber assembly to prevent the valve from opening for a short period of time when the valve is subjected to a sudden or rapid pressure rise, such as occurs in a surge of the fluid retained in such tanks.
2. Description of the Prior Art
Tanks for retaining fluid, particularly flammable or corrosive liquids, commonly are provided with a pressure relief valve so as to limit the internal pressure in the tank to a predetermined value for safety. Under normal conditions when the pressure inside the tank rises slowly as in normal storage of flammable liquids, such valves are opened at a predetermined pressure so as to relieve the excess pressure in the tank by venting to atmosphere. Thereafter, when the pressure inside of the tank is reduced to a safe level, the valve is closed to maintain the tank under desired pressure. Illustrations of prior art pressure relief valves are contained in the following patents:
______________________________________ U.S. Pat. No.: 1,893,942 3,845,876 1,942,630 3,854,623 2,016,278 3,913,601 2,847,149 3,938,692 3,186,682 3,945,395 3,580,275 3,974,850 3,365,096 4,287,910 3,744,670 4,593,711 3,757,987 British Patent: 1,285,733 ______________________________________
In addition to providing such a pressure relief valve for flammable or corrosive liquid tanks, it is desirable to include structure to temporarily prevent or control spillage or release of gases from within the tank in the event of a sudden pressure rise or surge of such liquid. Such surge control structure ideally is operable to maintain the pressure relief valve in closed condition for a short period of time to prevent spillage of the tank contents which normally would occur in prior art valves which do not include such surge control feature. Spillage or release of liquid might occur if a tank is upset or rolled over, such as in an accident, creating a sudden pressure rise resulting from liquid surge.
The valve of the present invention includes structure to impede or slow the rate at which pressure can build within the valve upon sudden pressure rise within the tank and thereby increase the time before which gases or liquid within the tank can escape to atmosphere in the event of such occurrence.